Illumination system and projection system incorporating the same

ABSTRACT

An illumination system and a projection system incorporating same are disclosed. The illumination system includes a two-dimensional array of independently operable light sources. Each light source illuminates substantially the entire active area of a pixelated optical light modulator. Each light source emits light in different emission directions. Each emission direction is directed to a respective location in the active area. Each pixel in the active area is illuminated by an incident cone of light from the two-dimensional array of independently operable light sources. The cone has a cone angle and includes at least one light ray from each light source. The cone angle of at least one such cone of light can be controlled by adjusting the intensity of one or more of the independently operable light sources.

CROSS REFERENCE

This application is a continuation of U.S. application Ser. No.11/215,770, filed Aug. 29, 2005now U.S. Pat. No. 7,438,423, now allowed;the disclosure of which is incorporated by reference in its entiretyherein.

FIELD OF THE INVENTION

This invention generally relates to illumination systems. The inventionis particularly applicable to illumination systems producing highcontrast in projection systems.

BACKGROUND

Illumination systems typically include a light source and illuminationoptics for transferring light from the light source to a desireddestination. Illumination systems are employed in various applications,such as projection displays and backlights for liquid crystal displays(LCD). The light source in an illumination system may, for example,include an arc lamp such as a mercury arc lamp, an incandescent lamp, afluorescent lamp, a light emitting diode (LED), or a laser.

Projection systems typically include an active light valve for producingan image, an illumination system for illuminating the light valve, andoptics for projecting and displaying the image typically on a projectionscreen. The illumination system in a projection system typically usesone or more white light sources, such as arc lamps. The illuminationoptics of the illumination system may include means for separating thewhite light into different colors, such as red, green, and blue.

It is often desirable to illuminate the light valve in such a way so asto display a projected image with high brightness, resolution andcontrast.

SUMMARY OF THE INVENTION

Generally, the present invention relates to illumination systems. Thepresent invention also relates to illumination systems employed inprojection systems.

In one embodiment of the invention, an illumination system includes aplurality of discrete light sources. The output light intensity of eachdiscrete light source can be individually controlled. The illuminationsystem further includes an aperture stop that is positioned in aconjugate plane of the plurality of discrete light sources. The aperturestop has an opening. Light from the plurality of discrete light sourcesfills at least a portion of the opening and forms a first optical fieldat the aperture stop. The illumination system further includes apixelated light modulator that has an active area capable of displayinga projectable image. The first optical field illuminates the active areaand forms a second optical field at the active area. The first andsecond optical fields form a Fourier transform pair. The contrast ratioof the projectable image can be adjusted by selectively controlling theoutput intensity of one or more of the discrete light sources.

In another embodiment of the invention, an illumination system includesa two-dimensional array of independently operable light elements. Theillumination system further includes a first optical transfer system.The first optical transfer system receives light from the light elementsand illuminates an active area of a pixelated light modulator. Theactive area is capable of displaying a projectable image. Light from atleast one light element illuminates the active area from a finite numberof directions. Each pixel in the active area is illuminated by eachlight element. The contrast ratio of the projectable image can becontrolled by adjusting the output intensity of one or more of the lightelements.

In another embodiment of the invention, an illumination system includesa two-dimensional array of independently operable light sources. Eachlight source is capable of illuminating substantially the entire activearea of a pixelated optical light modulator. Each light source emitslight in different emission directions. Each emission direction isdirected to a respective location in the active area. Each pixel in theactive area is illuminated by an incident cone of light from thetwo-dimensional array of independently operable light sources. The conehas a cone angle and includes at least one light ray from each lightsource. The cone angle of at least one such cone of light can becontrolled by adjusting the intensity of one or more of theindependently operable light sources.

In another embodiment of the invention, an illumination system includesan extended light source that is capable of emitting light withadjustable two-dimensional intensity profile. The illumination systemfurther includes a light modulator that has an active area capable ofdisplaying an image. A point in the extended light source illuminatesthe entire active area from the same direction. The direction isdifferent for different points in the extended light source. A contrastof the displayed image can be controlled by adjusting thetwo-dimensional intensity profile of the emitted light.

In another embodiment of the invention, a projection system includes aplurality of discrete light sources that are capable of illuminating theactive area of a pixelated light modulator to form a projectable imagehaving a contrast ratio. Each discrete light source illuminatessubstantially the entire active area. The projection system furtherincludes a processor for controlling the output light intensity of eachdiscrete light source individually. The processor further determines thecontrast ratio that corresponds to each discrete light source. Theprocessor further determines the average brightness of the projectableimage. When the average brightness is less than a threshold value, theprocessor reduces the output light intensity of one or more discretelight sources that have low contrast ratios to increase the contrastratio of the projectable image.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood and appreciated inconsideration of the following detailed description of variousembodiments of the invention in connection with the accompanyingdrawings, in which:

FIG. 1 shows a schematic three-dimensional view of an illuminationsystem in accordance with one embodiment of the invention;

FIGS. 2 a and 2 b show two exemplary cross-sectional intensity profilesfor the extended light source of FIG. 1;

FIG. 3 shows a schematic side-view of an illumination system inaccordance with one embodiment of the invention;

FIGS. 4 a-4 e show exemplary light cones according to the invention;

FIG. 5 shows another exemplary light cone according to the invention;

FIGS. 6 a-6 c show schematic front-view of exemplary light assemblies inaccordance with different embodiments of the invention;

FIG. 7 shows a schematic three-dimensional view of a projection displayin accordance with one embodiment of the invention;

FIGS. 8 a and 8 b show exemplary illumination directions according tothe invention;

FIG. 9 shows additional exemplary illumination directions according tothe invention;

FIG. 10 shows a schematic side-view of an optical transfer system inaccordance with one embodiment of the invention;

FIG. 11 shows a schematic side-view of an optical transfer system inaccordance with another embodiment of the invention;

FIG. 12 shows a schematic side-view of an optical transfer system inaccordance with another embodiment of the invention;

FIG. 13 shows a schematic side-view of an optical transfer system inaccordance with yet another embodiment of the invention;

FIG. 14 shows a schematic side-view of a projection display inaccordance with one embodiment of the invention;

FIG. 15 shows a schematic side-view of an optical transfer system inaccordance with one embodiment of the invention;

FIG. 16 shows a schematic side-view of a projection display inaccordance with one embodiment of the invention;

FIGS. 17 a and 17 b show schematic front-view of exemplary light sourcesin accordance with different embodiments of the invention;

FIG. 18 shows a schematic side-view of an illumination system inaccordance with one embodiment of the invention;

FIG. 19 shows a schematic side-view of a projection system in accordancewith one embodiment of the invention; and

FIG. 20 shows a schematic side-view of a projection system in accordancewith another embodiment of the invention.

DETAILED DESCRIPTION

The present invention generally relates to illumination systems. Theinvention is also applicable to projection systems that include anillumination system where it is desirable to display a projected imagewith high contrast and brightness. The invention is particularlyapplicable to projection systems that include a liquid crystal display(LCD) or a digital micro-mirror device (DMD) for producing a projectableimage.

In the specification, a same reference numeral used in multiple figuresrefers to the same or similar elements having the same or similarproperties and functionalities.

An advantage of the invention is that the light intensity profile of theillumination system can be dynamically controlled to optimize thecontrast and/or brightness of each or a sequence of projected imagesdepending, for example, on an overall brightness of the projected image.For example, the illumination system can be dynamically controlled toprovide maximum brightness for a bright projected image, such as anoutdoor day scene, and provide optimum contrast for a relatively darkprojected image, such as a night scene.

FIG. 1 illustrates a schematic three-dimensional view of an illuminationsystem 100 in accordance with one embodiment of the invention.Illumination system 100 includes a light assembly 110 and a lightmodulator 130. Light assembly 110 includes an extended light source 115that emits light for illuminating light modulator 130.

According to one aspect of the invention, extended light source 115emits light in different emission directions such as directions denotedby rays 112A, 112B, and 112C. The two-dimensional intensity profile ofextended light source 115, for example, in the xy-plane, can becontrolled by electronics 105 along one or more directions in thexy-plane. For example, the intensity profile can be controlled byelectronics 105 along directions A1-A2 and B1-B2, as schematicallyillustrated in FIGS. 2 a and 2 b. FIG. 2 a shows intensity, I, in thexy-plane as a function of location along the x-direction, and FIG. 2 bshows intensity as a function of location along the y-direction. Inparticular, FIG. 2 a illustrates exemplary intensity profiles 210 and211 along A1-A2 direction, and FIG. 2 b illustrates exemplary intensityprofiles 220 and 221 along B1-B2 direction. Intensity profiles 210 and220 can correspond to one configuration of electronics 105, andintensity profiles 211 and 221 can correspond to a differentconfiguration of electronics 105. It will be appreciated that directionsA1A2 and B1B2 are merely illustrative directions. In general, accordingto one aspect of the invention, electronics 105 is capable of energizingextended light source 115 so as to produce a desired two-dimensionalintensity profile in the xy-plane.

Referring back to FIG. 1, light modulator 130 has an active area 140that is capable of displaying an image. According to one aspect of theinvention, every light emitting point in extended light source 115illuminates substantially the entire active area 140. For example, eachof light emitting points 113 and 114 in extended light source 115illuminates substantially the entire active area 140. Furthermore, eachindividual light emitting point in extended light source 115 illuminatesactive area 140 from a common direction, where the common direction canbe different for different light emitting points. For example, lightemitting point 113 in extended light source 115 emits a cone of light117 having a solid cone angle α. Cone 117 includes exemplary light rays113A, 113B, and 113C. Light cone 117 illuminates active area 140 from acommon direction “U.” In particular, emitted light ray 113A illuminatesactive area 140 as light ray U1, emitted light ray 113B illuminatesactive area 140 as light ray U2, and emitted light ray 113C illuminatesactive area 140 as light ray U3, where rays U1, U2, and U3 are all alongthe common direction “U.” As another example, light emitting point 114illuminates active area 140 along direction “V” with exemplary lightrays V1, V2, and V3, where direction “V” is different than direction“U.”

Illumination system 100 may further include other components notexplicitly shown in FIG. 1. For example, illumination system 100 mayinclude an optical module positioned between light assembly 110 andlight modulator 130 for transferring light from the light assembly tothe modulator. In particular, the optical module may be designed, forexample, to redirect light rays in cone 117 so that they illuminatesubstantially the entire active area 140 along the common direction “U.”

Light modulator 130 can be any light modulator that is capable ofdisplaying an image. For example, light modulator 130 may be aMicroelectromechanical system (MEMS) such as a digital micro-mirrordevice (DMD). A DMD typically includes an array of tiltablemicro-mirrors. The tilt of each mirror can be independently controlledby, for example, an electrical signal. The tilting of each mirror (orpixel) allows the mirror to act as a fast and precise light switch. As aresult, a DMD can act as a spatial light modulator digitally modulatingan incident light to, for example, display an image when illuminatedwith an incident light. An example of a DMD is a Digital LightProcessor™ (DLP™) available from Texas Instruments Company, Dallas, Tex.

Further examples of light modulator 130 include a grating light valve(GLV) discussed, for example, in U.S. Pat. No. 5,841,579, or a liquidcrystal display (LCD). An LCD type modulator 130 can, for example, beoptically transmissive or reflective, such as a high temperaturepolysilicon (HTPS) LCD or a liquid crystal on silicon (LCOS) display,respectively. In a typical LCD, a thin film of a liquid crystal fills agap between two substrates made of, for example, glass or plastic.Polarizing sheets are usually placed on one or both sides of thesubstrates to polarize the light entering and exiting the liquidcrystal. The sides of the substrates facing the liquid crystal aretypically coated with patterned conductive electrodes that define anarray of liquid crystal cells or pixels. Application of an electricfield to the electrodes across a cell can affect optical transmission orreflection properties of the cell by changing the orientation of theliquid crystal molecules in the cell. The ability to affect opticalproperties of individual pixels allows the LCD to display an image whenilluminated with an incident light.

In general, light modulator 130 can be any electronically addressable orswitchable device capable of forming an image. In some applications,light modulator 130 may display a static image that can, for example, berefreshed, changed, or otherwise updated as a function of time dependingon the particular application.

Contrast ratio of a light modulator is usually defined as the ratio ofluminance or brightness between “white” (or “on”) and “dark” (or “off”or “black”) states in an active area of the modulator. There aredifferent methods for measuring contrast ratio, such as sequential andANSI (American National Standards Institute) contrast. In a sequentialcontrast ratio measurement, contrast ratio of a modulator, such asmodulator 130, is typically determined by measuring the brightness ofactive area 140, for example, at or near the center of the area, withthe entire active area displaying “white” (“on” state), followed bymaking a similar measurement with the entire active area displaying“black” (“off” or “dark” state). Contrast ratio is the ratio of the twomeasured values for brightness.

ANSI-contrast is measured by providing a 16 box (pixel) checkerboarddisplay made up of alternating “white” and “black” pixels. The luminanceof the “white” state is obtained by measuring and adding the brightnessat the centers of the eight “white” pixels. Similarly, the luminance ofthe “black” state is obtained by measuring and adding the brightness atthe centers of the eight “black” pixels. ANSI-contrast is the ratio ofthe two luminance values.

According to one aspect of the invention, the contrast ratio of an imagedisplayed in active area 140 can be controlled by adjusting thetwo-dimensional intensity profile of the emitted light. For example,referring again to FIGS. 2 a and 2 b, an intensity profile characterizedby intensity profiles 210 and 220 can result in an image displayed inactive area 140 having a contrast ratio that is different than acontrast ratio of the same image being displayed in the active area foran intensity profile characterized by intensity profiles 211 and 221.

One advantage of the present invention is that for a given lightmodulator and/or light source, the contrast ratio and/or brightness of adisplayed image can be improved or optimized by adjusting thetwo-dimensional intensity profile of extended light source 115.

Illumination system 100 may be advantageously employed in a front orrear projection system to provide improved contrast, resolution, andbrightness. An image formed by the projection system may be real orvirtual, in which case, a viewer may be able to view the image directlyor, for example, with an eyepiece.

FIG. 3 illustrates a schematic side-view of an illumination system 300in accordance with one embodiment of the invention. Illumination system300 includes a light assembly 310 and a pixelated light modulator 330having an active area 340. Light assembly 310 includes a two-dimensionalarray of independently operable light sources 315, such as light sources315A, 315B, and 315C. Each light source can be operated individually orindependently, meaning, for example, that the output light intensity ofeach independently operable light source can be adjusted independentfrom the output light intensity of other independently operable lightsources. For example, the output light intensity of light source 315Acan be different than the output light intensity of light source 315B,which in turn, can be different than the output light intensity of lightsource 315C. In some applications or under some circumstances, theoutput light intensity of one or more of the independently operablelight sources can be reduced, or minimized by, for example, turning offor otherwise blocking those particular light sources.

In one embodiment of the invention, each independently operable lightsource in light source 315 illuminates substantially the entire activearea 340. For example, independently operable light source 315Cilluminates substantially the entire active area 340. Furthermore, eachindependently operable light source emits light in different emissiondirections. For example, light source 315A emits light in differentemission directions such as light rays 318A and 318B emitted alongemission directions A and B, respectively; light source 315B emits lightin different emission directions such as light rays 316A and 316Bemitted along emission directions A and B, respectively; and lightsource 315C emits light in different emission directions such as lightrays 317A and 317B emitted along emission directions A and B,respectively. In addition, each emission direction is directed to arespective location in active area 340, meaning that all rays emitted ina given direction by light source 315 illuminate active area 340 in arespective location. For example, rays 316A, 317A, and 318A which areemitted along direction “A” converge to a same location in active area340, such as pixel 341A. As another example, rays 316B, 317B, and 318Bwhich are emitted along direction “B,” where direction “B” is differentthan direction “A,” converge to a different location in active area 340,such as pixel 341B.

Each pixel in the active area 340 is illuminated by an incident lightcone that has a cone angle and includes at least one light ray emittedfrom each independently operable light source in two-dimensional arrayof light sources 315. For example, pixel 341C in active area 340 isilluminated by light cone 320. Light cone 320 has a cone angle β. FIG. 3shows two exemplary extreme rays 320A and 320B in light cone 320. Lightcone 320 includes a plurality of light rays, where the pluralityincludes at least one light ray from each independently operable lightsource in two-dimensional array of light sources 315.

Cone angle β of light cone 320 can be controlled by adjusting the outputlight intensity of one or more of the independently operable lightsources in two-dimensional array of light sources 315. For example, bymodifying the output light intensity of one or more of the independentlyoperable light sources 315, light cone 320 can change to light cone 350with a cone angle γ, where γ is smaller than β.

In general, the contrast ratio of a light modulator decreases as thecone angle of an incident light cone illuminating the modulatorincreases. In the case of an LCD modulator, this decrease is typicallydue to the dependence of the liquid crystal material retardance on theincident angle of an incident light ray. Such dependence reduces thecontrast ratio by increasing the brightness of a pixel in the darkstate. Light leakage in the polarizing sheets (or other components suchas polarizing beam splitters) at oblique incident angles can alsocontribute to contrast degradation.

In the case of a DMD modulator, the decrease in the contrast ratio isbelieved to be, at least in part, due to optical diffraction effects. Inall light modulators, stray or scattered light originating, for example,from an imperfect lens surface can also reduce the contrast ratio.

One advantage of the present invention is that the contrast of an imagedisplayed by light modulator 330 can be increased by adjusting theoutput light intensities of the individual light sources intwo-dimensional array of light sources 315 so that one or more coneangles of incident light cones in active area 340 are reduced which can,for example, result in improved image contrast.

Furthermore, in one embodiment of the invention, the output intensity ofone or more light sources that do not significantly affect the size ofthe cone angle of an incident light cone may be increased to furtherimprove the contrast ratio and/or brightness of an image. Such lightsources can, for example, be light sources that contribute incidentlight rays that are located in the inner parts of an incident lightcone.

Illumination system 300 may further include other components notexplicitly shown in FIG. 3. For example, illumination system 300 mayinclude an optical component placed between light assembly 310 andpixelated light modulator 330 for transferring light from the lightassembly to the modulator. In particular, the optical component may bedesigned, for example, to redirect all rays emitted along direction “A”to pixel 341A and redirect all rays emitted along direction “B” to pixel341B.

Illumination system 300 may be advantageously employed in a front orrear projection system to provide improved contrast, resolution, andbrightness.

In the invention, a cone generally refers to a plurality of light raysdefining an inclusion angle, referred to as a cone angle. A generallight cone according to the invention is shown in FIG. 4 a where cone400 includes a plurality of light rays such as rays 400A, 400B, and400C, where the light rays define an inclusion solid angle or cone angleα₁. Cone 400 further has a base 410 in the xy-plane defined by anarbitrarily shaped closed curve 411. The base typically refers to a conecross-section along the z-axis where the light cone intersects a lightmodulator. In general, a cross-section of cone 400 at other locationsalong the z-axis may have a shape different than base 410. For example,cross-section 420 of cone 400 in the xy-plane has a different shape thanbase 410. Base 410 can, for example, illuminate a pixel in active area340 (see FIG. 3) or a location in active area 140 (see FIG. 1).

Other exemplary light cones are shown in FIGS. 4 b-4 e. For example,FIG. 4 b shows a cone 401 having an apex 412, a cone angle α₂, exemplaryoutermost light rays 401A, 401B, and 401C, and a cross-sectional profile421 in the xy-plane where profile 421 can, for example, be a circle oran ellipse or an arbitrary shape. It will be appreciated that a coneaccording to the invention can be a cone similar to cone 401 buttruncated near apex 412.

FIG. 4 c shows a cone 402 having a rectangular base 413, an inclusionsolid angle α₃, and exemplary outermost rays 402A, 402B, and 402C.Cross-section 422 is a cross-section of the cone in the xy-plane at adifferent location along the z-axis. As can be seen, cross-section 422has an arbitrary profile. Another exemplary cone is schematically shownin FIG. 4 d where cone 403 has a rectangular base 414, a cone angle α₄,and a cross-section 423 in the xy-plane at a different point along thez-axis that has a circular or elliptical profile. Base 413 or 414 can,for example, illuminate a pixel in active area 340 (see FIG. 3).

As yet another example, FIG. 4 e shows a cone 404 in the shape of atruncated pyramid, or a type of frustum, having a rectangular base 415and an inclusion angle α₅. Cone 404 has rectangular cross-sections alongother points along the z-axis, such as cross-section 424. Base 415 can,for example, illuminate a pixel in active area 340 (see FIG. 3).

In general, the base of a cone or other cross-sections of the cone inthe xy-plane can have any two-dimensional shape that may be desirable ina particular application. Exemplary shapes include a circle, an ellipse,a polygon such as a quadrilateral, a rhombus, a parallelogram, atrapezoid, a rectangle, a square, or a triangle, or any other shape thatmay be advantageous in a given application. For example, referring backto FIG. 3, the shape of the base of light cone 320 may be designed tosubstantially match the shape of pixel 341C, the pixel illuminated bythe light cone. Shape matching can increase the contrast and/orbrightness of a displayed image.

The exemplary cones shown in FIGS. 4 a-4 e can be solid or can havesections devoid of light rays. One such example is shown in FIG. 5. Cone500 includes a plurality of light rays such as rays 500A, 500B, 500C,and 500D. The plurality of light rays defines an inclusion solid angleor cone angle α₆. Cone 500 further has a rectangular base 510 in thexy-plane with an open area 511. Cross-section 520 is a cross-section ofcone 500 in the xy-plane at a point along the z-axis other than thepoint corresponding to base 510. Cross-section 520 has an open area 530.As shown in FIG. 5, cone 500 has a single open section 540 that includesno light rays. In general, cone 500 can have more than one open section.

Referring back to FIG. 3, array of light sources 315 can include anytype of light sources that may be advantageous in an application.Examples include an arc lamp such as a mercury arc lamp, an incandescentlamp, a fluorescent lamp, a laser, a light emitting diode (LED), organiclight emitting diodes (OLED), vertical cavity surface emitting lasers(VCSEL), or any other suitable light emitting devices.

In one preferred embodiment of the invention, each light source intwo-dimensional array of light sources 315 is an LED.

The independently operable light sources in array 315 can be arranged inany form of an array that may be desirable in an application. Examplesinclude rectangular, triangular, hexagonal, circular, or any othersuitably configured arrays. FIGS. 6 a-6 c show schematic front-view ofthree exemplary light assemblies having different arrays ofindependently operable light sources. FIG. 6 a shows a light sourceassembly 610 that includes a two-dimensional rectangular array ofindependently operable light sources 615. Light source 616A is anexemplary independently operable light source in the array of lightsources. FIG. 6 b shows a light source assembly 620 that includes atwo-dimensional circular array of independently operable light sources625. Light source 626A is an exemplary independently operable lightsource in the array of light sources. Similarly, FIG. 6 c shows a lightsource assembly 630 that includes a two-dimensional array ofindependently operable light sources 635. Light source 636A is anexemplary independently operable light source in the array of lightsources. It will be appreciated that according to the present invention,the array of independently operable light sources may include differentsize light sources. For example, in array of light sources 635, lightsource 636B has a larger area than light source 636C.

In one embodiment of the invention, the individual light sources can beof different types. For example, some of the light sources can be LEDsand some others can be arc lamps, and still some other light sources inthe array can be OLEDs. Furthermore, the emission spectra of the lightsources can be different. For example, in an array of independentlyoperable LEDs, different LEDs can emit different color light such aswhite, green, red, and blue.

FIG. 7 illustrates a schematic three-dimensional view of a projectiondisplay 700 in accordance with another embodiment of the invention.Projection display 700 includes an illumination system 701 and aprojection system 702. Illumination system 701 includes an extendedlight source 710, a first optical transfer system 720 and a pixelatedlight modulator 730.

Extended light source 710 is centered on an optical axis 716 andincludes a two-dimensional array 715 of independently operable lightelements, such as light elements 715A and 715B. Each light element emitsa cone of light characterized by an output light intensity, a coneangle, and a central ray that propagates along a direction. For example,light element 715B emits a cone of light 703 that has a cone angle α₇,exemplary outermost rays 705A and 705B, and a central ray 705C thatpropagates along a direction 704.

First optical transfer system 720 receives light emitted by light source710 from its input face 721, transfers the received light to its outputface 722, and delivers the transmitted light from its output face topixelated light modulator 730.

According to one embodiment of the invention, light from at least onelight element that is transmitted by first optical transfer system 720illuminates pixelated light modulator 730 from a finite number ofdirections, where the finite number of directions is at least two. Forexample, first optical transfer system 720 receives cone of light 703from its input face 721, transmits the received light to its output face722 and delivers the transmitted light to modulator 730 along twodirections 717 and 719. For example, rays 716A and 716B originate fromcone 703, exit output face 722, and propagate towards modulator 730along direction 717. Similarly, rays 718A and 718B originate from cone703, exit output face 722, and propagate towards modulator 730 alongdirection 719.

According to one embodiment of the invention, directions 717 and 719 arerotationally symmetric about optical axis 716 as described in referenceto the schematics shown in FIGS. 8 a and 8 b. FIG. 8 a shows direction717 making an angle α₈ with optical axis 716 and direction 719 making anangle α₉ with optical axis 716, where α₈ and α₉ are equal. Furthermore,according to one embodiment of the invention, direction 704 is the sameas one of directions 717 and 719. For example, in FIG. 8 a direction 704is along direction 717.

As shown in FIG. 8 a, directions 717 and 719 and optical axis 716 neednot lie in the same plane. According to one embodiment of the invention,however, directions 717 and 719 and optical axis 716 lie in a same plane810, as shown schematically in FIG. 8 b.

Referring back to FIG. 7, optical transfer system 720 redirects cone 703so that all the cone rays exit the optical transfer system alongdirections 717 and 719. Light rays in a cone from some light elementsmay exit first optical transfer system 720 substantially along a singledirection. This may be the case, for example, for light elements thatare positioned near optical axis 716, such as light element 715C.

In general, light rays in a light cone, such as light rays in light cone703 from light element 715B can exit output face 722 of first opticaltransfer system 720 along a finite number of directions. An example isshown schematically in FIG. 9. In particular, FIG. 9 shows a lightelement 715D that emits a light cone 903 having a cone angle α₁₀ and acentral ray 915A that propagates along a direction 904. Light rays incone 903 exit first optical transfer system 720 along three differentdirections U1, U2, and U3 that are rotationally symmetric about opticalaxis 716, meaning that angles ω₁, ω₂, and ω₃ are equal, where ω₁ is theangle between direction U1 and optical axis 716, ω₂ is the angle betweendirection U2 and optical axis 716, and ω₃ is the angle between directionU3 and optical axis 716. According to one embodiment of the invention,direction 904 is the same as one of three directions U1, U2, and U3.

Referring back to FIG. 7, pixelated light modulator 730 has an activearea 740 that includes an array of individually controllable pixels,such as pixels 751 and 752. Active area 740 is capable of displaying animage when illuminated with light delivered by first optical transfersystem 720. In general, light modulator 730 can be any electronicallyaddressable or switchable device capable of forming an image, such as anLCD or a DMD. In one embodiment of the invention, each pixel in lightmodulator 730 provides a higher contrast ratio as the cone angle of anincident cone of light illuminating the pixel is reduced.

First optical transfer system 720 can include one or more opticalcomponents such as a lens, a micro lens array, a light homogenizer, anoptical filter, a color wheel, a mirror, or any other optical componentthat may be used in first optical transfer system 720 to transfer lightto light modulator 730 according to the invention.

An exemplary first optical transfer system 720 is optical transfersystem 1300 shown schematically in FIG. 10. Optical transfer system 1300is positioned between two-dimensional array of independently operablelight elements 715 and pixelated light modulator 730 having an activearea 740. For ease of illustration and without loss of generality, onlythree light elements 715A, 715B, and 715C of array 715 are shown.Optical transfer system 1300 includes a first lens array 1305, a secondlens array 1315, and a field lens 1330. Each light element has adedicated lens from first lens array 1305 and a dedicated lens fromsecond lens array 1315. For example, light element 715A has dedicatedlenses 1310 and 1320. Optical transfer system 1300 redirects light fromeach light element so that light out put from each light elementilluminates substantially the entire active area 740 from a finitenumber of directions. For example, light element 715-A emits a cone oflight 1360. Lenses 1310, 1320, and 1330 act cooperatively to redirectlight rays in light cone 1360 to illuminate the entire active area 740along direction 1370 as exemplified by light rays 1371 and 1372.

Another exemplary first optical transfer system 720 is optical transfersystem 1400 shown schematically in FIG. 11. Optical transfer system 1400is positioned between two-dimensional array of independently operablelight elements 715 and pixelated light modulator 730 having an activearea 740. In the example of FIG. 11, each light element includes adedicated lens cap for reducing the cone angle of the light cone emittedby the light element. For example, light element 715A includes a lenscap 1430. Optical transfer system 1400 includes a lens array 1405, acondenser lens 1410 and an optional field lens 1420. Each light elementhas a dedicated lens from lens array 1405. For example, light element715A has a dedicated lens 1406. Optical transfer system 1400 redirectslight from each light element so that light output from each lightelement illuminates substantially the entire active area 740 from afinite number of directions. For example, light element 715A emits acone of light 1460. Lenses 1406, 1410, and 1420 act cooperatively toredirect light rays in light cone 1460 to illuminate the entire activearea 740 along direction 1470 as exemplified by light rays 1471 and1472. Optional field lens 1420 can make illumination system 1490telecentric, meaning that one or both of an entrance pupil and an exitpupil of illumination system 1490 can be located at or near infinity.

Optical transfer system 1400 further directs lights rays emitted byarray 715 so that light rays emitted in a same direction are directed tosubstantially a same location in active area 740. For example, lightrays 1431, 1432, and 1433 are emitted by different light elements alonga same direction 1480. Optical transfer system 1400 redirects theselight rays so that they converge substantially to a same point 1491 inactive area 740.

Another exemplary first optical transfer system 720 is optical transfersystem 1600 shown schematically in FIG. 12. Optical transfer system 1600is positioned between two-dimensional array of independently operablelight elements 715 and pixelated light modulator 730 having an activearea 740. For simplicity and without loss of generality, only threelight elements 715A, 715B, and 715C of array 715 are shown. Opticaltransfer system 1600 includes a first lens array 1605, a second lensarray 1615, a light homogenizer 1650, and a relay lens system 1625 thatincludes lenses 1630 and 1640. Each light element has a dedicated lensfrom first lens array 1605 and a dedicated lens from second lens array1615. For example, light element 715A has dedicated lenses 1610 and1620. Optical transfer system 1600 redirects light from each lightelement so that light output from each light element illuminatessubstantially the entire active area 740 from a finite number ofdirections. For example, light element 715A emits a cone of light 1660.Optical transfer system 1600 redirects light rays in light cone 1660 toilluminate the entire active area 740 along directions 1671 and 1672,where these two directions can be rotationally symmetric about opticalaxis 716.

Homogenizer 1650 is designed to homogenize light received fromtwo-dimensional array of independently operable light elements 715. Forexample, homogenizer 1650 homogenizes light received from light element715A, where by homogenizing it is meant that light exiting homogenizer1650 has a more uniform spatial intensity distribution than lightentering homogenizer 1650. Examples of known light homogenizers may befound in U.S. Pat. Nos. 5,625,738 and 6,332,688; and U.S. PatentApplication Publication Nos. 2002/0114167, 2002/0114573, and2002/0118946.

Homogenizer 1650 has an input face 1651, an optical rod 1653 and anoutput face 1652. Input face 1651 may or may not be parallel to outputface 1652. In general, output face 1652 may have a shape that isdifferent than the shape of active area 740. For example, output face1652 may be a trapezoid and active area 740 may be a square. In someapplications, output face 1652 and active area 740 may have the sameshape, such as a rectangle or a square.

Input face 1651, output face 1652, and a cross-section of optical rod1653 can have any shape such as a rectangle, a trapezoid, a square, anellipse or any other shape that may be desirable in an application.Input face 1651, output face 1652, and a cross-section of optical rod1653 can have different shapes. For example, input face 1651 can be acircle, while output face 1652 can be a square. A cross-section ofoptical rod 1653 can be different at different locations along theoptical rod. For example, optical rod 1653 may be tapered along itslength along optical axis 716. The sides of a cross-section of opticalrod 1653 may be straight or curved. An example of a tapered optical rodis described in U.S. Pat. No. 6,332,688.

Homogenizer 1650 can have any three-dimensional shape, for example, apolyhedron, such as a hexahedron. A portion of or the entire homogenizer1650 can be solid or hollow. Homogenizer 1650 may homogenize an inputlight by any suitable optical method such as reflection, total internalreflection, refraction, scattering, or diffraction, or any combinationthereof.

Another exemplary first optical transfer system 720 is optical transfersystem 1700 shown schematically in FIG. 13. Optical transfer system 1700is positioned between two-dimensional array of independently operablelight elements 715 and pixelated light modulator 730 having an activearea 740. For simplicity and without loss of generality, only threelight elements 715A, 715B, and 715C of array 715 are shown. Opticaltransfer system 1700 includes a plurality of light guides 1701, aplurality of lens caps 1702, a lens array 1704, a condenser lens 1710,and a field lens 1720. Each light element has a dedicated light guidefrom plurality of light guides 1701, a dedicated lens cap from pluralityof lens caps 1702, and a dedicated lens from lens array 1704. Forexample, light element 715A has dedicated light guide 1701A, lens cap1702A, and lens 1704A, where in the example of FIG. 13, lens cap 1702Ais mounted on the output face 1760 of light guide 1701A. Opticaltransfer system 1700 redirects light from each light element so thatlight output from each light element illuminates substantially theentire active area 740 from a finite number of directions. For example,optical transfer system 1700 redirects light rays emitted by lightelement 715A to illuminate the entire active area 740 along directions1731 and 1732, where these two directions can be rotationally symmetricabout optical axis 716.

Optical transfer system 1700 further includes an aperture stop 1705positioned at or near lens array 1704. In the embodiment shown in FIG.13, the output face of each light guide of plurality of light guides1701 is imaged onto substantially the entire active area 740. Forexample, output face 1760 is imaged onto substantially the entire activearea 740.

Referring back to FIG. 7, projection system 702 includes a secondoptical transfer system 750 and a projection screen 760. Second opticaltransfer system 750 projects an image formed by light modulator 730 ontoprojection screen 760. FIG. 7 shows an optically transmissive lightmodulator 730. In general, light modulator 730 may be transmissive orreflective. A projection display similar to projection display 700, butemploying a reflective light modulator, is schematically shown in FIG.14. In particular, FIG. 14 shows a reflective pixelated light modulator1030 that receives light in a general direction W1 and selectivelyreflects the received light in a general direction W2 towards secondoptical transfer system 750 for projection onto projection screen 760.

Referring back to FIG. 7, projection display 700 may be a rearprojection system, in which case, projection screen 760 is a rearprojection screen. Projection display 700 may be a front projectionsystem, in which case, projection screen 760 is a front projectionscreen.

Second optical transfer system 750 can include one or more opticalcomponents such as a lens, a micro lens array, a polarizer, a colorcombiner, a mirror, a Fresnel lens, or any other optical component thatmay be used in second optical transfer system 750 to project an imagedisplayed by light modulator 730 (or 1030) onto screen 760 according tothe invention.

An exemplary second optical transfer system 750 is optical transfersystem 1500 shown schematically in FIG. 15. Optical transfer system 1500is placed between pixelated light modulator 730 and projection screen760 and includes a plurality of lens elements, in particular, lenselements 1510, 1520, 1530, 1540, and 1550. Optical transfer system 1500magnifies and projects an image displayed in active area 740 ontoprojection screen 760. Other examples of known projection systems arediscussed in U.S. Pat. Nos. 6,417,971; 6,301,057; and 5,969,876.

FIG. 16 shows a schematic side-view of a projection display 1100 inaccordance with another embodiment of the invention. Projection display1100 includes an illumination system 1101 and a projection system 1102.Illumination system 1101 is primarily designed to illuminate an imageforming modulator 1160, and projection system 1102 is primarily designedto project an image formed by modulator 1160 onto a projection screen1190, for example, for viewing by a viewer 1195.

Illumination system 1101 includes an extended light source 1110, a firstoptical transfer system 1120, an aperture stop 1130, a second opticaltransfer system 1150 and a pixelated light modulator 1160. Extendedlight source 1110 includes a plurality of discrete light sources 1115,such as discrete light source 1111. Each of the discrete light sourcescan be controlled individually, meaning that, for example, the outputintensity of each discrete light sources can be controlled independentfrom other discrete light sources. In some applications, it may beadvantageous to control different subsets of plurality of discrete lightsources 1115 as discrete groups as described in more detail in referenceto FIGS. 17 a and 17 b.

FIG. 17 a shows a front view schematic of a plurality of discrete lightsources 1215 similar to light sources 1115 in FIG. 16 in accordance toone embodiment of the invention. Plurality of discrete light sources1215 includes a first circular row 1220 of discrete light sources, suchas discrete light source 1220A, that are connected to each other byelectrical connectors 1222. All the discrete light sources in firstcircular row 1220 can be energized as a group by electronics 1221.Plurality of discrete light sources 1215 further includes a secondcircular row 1230 of discrete light sources, such as discrete lightsource 1230A, that are connected to each other by electrical connectors1232. All the discrete light sources in second circular row 1230 can beenergized as a group by electronics 1231. Plurality of discrete lightsources 1215 further includes a third circular row 1240 of discretelight sources, such as discrete light source 1240A, that are connectedto each other by electrical connectors 1242. All the discrete lightsources in third circular row 1240 can be energized as a group byelectronics 1241. In general, plurality of discrete light sources 1215can have more or fewer rows of light sources. In the exemplarytwo-dimensional light source shown in FIG. 17 a, the output intensity ofeach row can be controlled individually. In general, light source 1215can include different segments, where the output light intensity of eachsegment can be controlled individually.

FIG. 17 b shows a front view schematic of a plurality of discrete lightsources 1250 in accordance to one embodiment of the invention. Pluralityof discrete light sources 1250 includes 16 discrete light segmentsnumbered from 1 to 16. Each light segment is individually controlled by,for example, a dedicated electronics circuitry. For example, electronics1212 controls the output light intensity of light segment 12, andelectronics 1209 controls the output light intensity of light segment 9.

Referring back to FIG. 16, plurality of discrete light sources 1115 isshown to be non-planar. In general, plurality of discrete light sources1115 can be arranged in any configuration that may be advantageous in agiven application. For example, plurality of discrete light sources 1115may be arranged to form a spherical, ellipsoidal, parabolic, hyperbolic,planar, or any other suitable surface. As another example, plurality ofdiscrete light sources 1115 can be arranged to form at least a portionof a polyhedron, such as a tetrahedron, a hexahedron, an octahedron, adodecahedron, an icosahedron, or any other multifaceted surface. Stillas another example, different light sources in plurality of discretelight sources 1115 may be arranged in different ways. For example, theinner light sources may form a portion of a polyhedron, and the outerlight sources may form a portion of a spherical surface. The sphericalsurface may furthermore be positionally offset from the polyhedron so asto form two discrete sets of light sources.

According to one embodiment of the invention, the plurality of discretelight sources 1115 may include different size light sources. Forexample, referring to FIG. 17 b, light source 10 has a larger area thanlight source 16. The light sources in plurality of discrete lightsources 1115 can be of different types. For example, some of the lightsources can be LEDs and some others can be arc lamps, and still someother light sources can be OLEDs. Furthermore, the emission spectra ofthe light sources can be different. For example, in a plurality ofdiscrete LEDs, different LEDs can emit different color light such aswhite, green, red, or blue.

Aperture stop 1130 has an open area 1140 that is optically transmissive.Opening area 1140 may be in the form of a square, circle, ellipse,trapezoid, or any other shape that may be suitable in an application.Furthermore, the size of opening 1140 can be controlled, for example,manually or electronically.

First optical transfer system 1120 images plurality of discrete lightsources 1115 in a plane that substantially coincides with or issubstantially close to the plane of aperture 1130. The formed image is afirst optical field 1145 that fills at least a portion of apertureopening 1140. In one embodiment of the invention, first optical field1145 substantially fills the entire aperture opening 1140. Optical field1145 and plurality of discrete light sources 1115 form a conjugate pair,meaning that, for example, optical field 1145 lies in an image plane ofplurality of discrete light sources 1115.

One advantage of the present invention is dynamic apodization, meaningthat by individual control of discrete light sources in plurality ofdiscrete light sources 1115, the effective shape and/or size of aperturestop 1130 can be dynamically controlled resulting in improved brightnessand/or contrast of a projected image.

First optical transfer system 1120 can include one or more opticalcomponents such as a lens, a micro lens array, a light homogenizer, anoptical filter, a color wheel, a mirror, a Fresnel lens, or any otheroptical component that may be suitably used in first optical transfersystem 1120 to image plurality of discrete light sources 1115 ontoaperture opening 1140.

Pixelated light modulator 1160 has a pixelated active area 1170,including pixels such as pixel 1171, that is capable of forming animage. Second optical transfer system 1150 transfers first optical field1145 onto active area 1170, thus forming a second optical field 1165 inthe plane of active area 1170 or pixelated light modulator 1160.According to one embodiment of the invention, first optical field 1145and second optical field 1165 form a Fourier transform pair, meaningthat, in general, every point in optical field 1145 illuminatessubstantially the entire active area 1171 from a finite number ofdirections, preferably one or two directions. Furthermore, all lightrays from first optical field 1145 that propagate along a same directionconverge substantially at a respective point in active area 1170.

Second optical field 1165 may illuminate a portion of active area 1170,a situation that is sometimes referred to as an underfill. Secondoptical field 1165 may illuminate an area extending beyond active area1170, a situation that is sometimes referred to as an overfill.According to one embodiment of the invention, the size of second opticalfield 1165 is substantially the same as the size of active area 1170,meaning that there is minimized or no overfill or underfill.

Second optical transfer system 1150 can include one or more opticalcomponents such as a lens, a micro lens array, a light homogenizer, anoptical filter, a color wheel, a mirror, a Fresnel lens, or any otheroptical component that may be suitably used in second optical transfersystem 1150 to receive first optical field 1145 and form a secondoptical field 1165 at modulator 1160 where the two optical fields form aFourier transform pair.

An exemplary first optical transfer system 1120 and second opticaltransfer system 1150 is shown in FIG. 18. FIG. 18 shows a schematicside-view of an illumination system 1900 in accordance with oneembodiment of the invention. Illumination system 1900 includes aplurality of discrete light sources 1115. For simplicity and withoutloss of generality, plurality of discrete light sources 1115 includesthree light sources 1115A, 1115B, and 1115C. In general, plurality ofdiscrete light sources 1115 can include an array of discrete lightsources arranged as required by the application. Illumination system1900 further includes a pixelated light modulator 1160 having an activearea 1170. Illumination system 1900 further includes a first pluralityof discrete lenses 1910, a second plurality of discrete lenses 1920, anaperture stop 1930, a condenser lens 1940, and a field lens 1980. Eachdiscrete light source has a dedicated lens from first plurality ofdiscrete lenses 1910 and a dedicated lens from second plurality ofdiscrete lenses 1920. For example, light source 1115A has dedicatedlenses 1910A and 1920A. Second plurality of discrete lenses 1920 arepositioned in opening 1931 of aperture stop 1930. According to theexemplary embodiment shown in FIG. 18, aperture stop 1930 is positionedin a conjugate plane of plurality of light sources 1115. For example,light source 1115A is imaged in opening 1931 of aperture stop 1930.Light from plurality of light sources 1115 forms a first optical field1990 in opening 1931. According to one embodiment of the invention,light from each discrete light source illuminates substantially theentire active area 1170 in a same direction. For example, light emittedby discrete light source 1115A illuminates substantially the entireactive area 1170 in a direction 1950 as exemplified by light rays 1951,1952, and 1953. Furthermore, according to one embodiment of theinvention, light rays that exit opening 1931 of aperture 1930 in a givendirection are directed to a same location in active area 1170. Forexample, light rays 1961, 1962, and 1963 exit opening 1931 of aperturestop 1930 along direction 1960. These rays subsequently converge at asame location 1970 in active area 1170. According to one embodiment ofthe invention, first optical field 1990 illuminates substantially theentire active area 1170 and forms a second optical field 1991 at theactive area, where the two optical fields form a Fourier transform pair.

Referring back to FIG. 16, projection system 1102 includes a thirdoptical transfer system 1180 and a projection screen 1190. Third opticaltransfer system 1180 projects an image formed by light modulator 1160onto projection screen 1190. FIG. 16 shows an optically transmissivelight modulator 1160. In general, as discussed previously, lightmodulator 1160 may be optically transmissive or reflective.

Projection display 1100 may be a rear projection system, in which case,projection screen 1190 is a rear projection screen. Projection display1100 may be a front projection system, in which case, projection screen1190 is a front projection screen.

Third optical transfer system 1180 can include one or more opticalcomponents such as a lens, a micro lens array, a polarizer, a colorcombiner, a mirror, a Fresnel lens, an aperture stop, or any otheroptical component that may be suitably used in third optical transfersystem 1180 to project an image displayed by light modulator 1160 ontoscreen 1190. An example of third optical transfer system 1180 is shownin FIG. 15.

Projection display 1100 further includes a processor 1103 for measuringand storing the contrast ratio corresponding to each discrete lightsource. This can be done by, for example, turning off all but one of thediscrete light sources, and measuring the contrast ratio in active area1170 corresponding to “on” light source. Such a measurement can be madefor each light source resulting in an electronically stored look-uptable ranking the discrete light sources from having the worst orsmallest contrast ratio to the best or highest contrast ratio.

Processor 1103 can also measure an average brightness of a projectableimage formed in active area 1170 where the projectable image can, forexample, be projected onto projection 1190 by third optical transfersystem 1180. The measured average brightness can be used by processor1103 to increase the contrast ratio and/or brightness of the projectableimage by adjusting the output intensity of one or more discrete lightsources. For example, when the average brightness is lower than athreshold value signaling a relatively dark image such as a night scene,processor 1103 may reduce the output intensity of or completely turn offone or more of the independent light sources that have the lowestcorresponding contrast ratios. The affected discrete light sources canbe in the outer part of the plurality of discrete light sources 1115, inthe inner part, or in general positioned at different locations in theextended light source 1110. An advantage of the invention is that theoutput intensity of a discrete light source can be controlledindividually to improve the contrast ratio and/or brightness of aprojectable image regardless of the location of the discrete lightsource. At the same time, processor 1103 can increase the outputintensity of one or more discrete light sources that have correspondinghigh contrast ratios. Therefore, the brightness and contrast of arelatively dark projectable image may be increased.

If the average brightness of a projectable image in active area 1170 ishigher than a threshold value signaling a bright image such as anoutdoor day image, processor 1103 may keep all discrete light sources1115 on, and may even increase the output intensities of one or more ofthe discrete light sources.

An advantage of the present invention is that processor 1103 can measurea contrast ratio for each discrete light source for any given activearea 1170 and any given plurality of light sources 1115. For example,the output intensity of a particular discrete light source that has acorresponding low contrast ratio can be reduced regardless of where thediscrete light source is located in extended light source 1110.Processor 1103 can be part of electronics 105 (see FIG. 1), in whichcase, the functions of processor 1103 can be carried out by electronics105.

FIG. 19 shows a side-view of a projection system 1800 in accordance withone embodiment of the invention. Projection system 1800 includes a firstillumination system 1801, a second illumination system 1802, and a thirdillumination system 1803, although, in general projection system 1800can have more or fewer illumination systems. Furthermore, although FIG.19 shows the three illumination systems generally arranged along x and ydirections, in general, each illumination system can be oriented in anydirection as required in a given application.

Each illumination system in FIG. 19 includes a two-dimensional array ofindependently operable light elements, a first lens array, a second lensarray, a field lens, and a light modulator having an active area that iscapable of displaying an image. For example, first illumination system1801 includes a first two-dimensional array of independently operablelight elements 1810, three of which (light elements 1801A, 1801B, and1801C) are shown in FIG. 19. In general, each two-dimensional array ofindependently operable light elements includes a plurality of lightsources arranged so as to optimally meet the needs in a givenapplication. Illumination system 1801 further includes a first lensarray 1820 and a second lens array 1830. Each light element in array1810 has a dedicated lens from first lens array 1820 and a dedicatedlens from second lens array 1830. For example, light element 1801C hasdedicated lenses 1820-C and 1830-C. Illumination system 1801 furtherincludes field lens 1840, and a light modulator 1850 that has an activearea 1851, where the active area is capable of displaying an image.Light modulator 1850 can be an LCD or any other light modulator capableof forming an image, examples of which have been previously discussed inthe specification.

According to one embodiment of the invention, light emitted by eachlight element illuminates substantially the entire active area of acorresponding light modulator. For example, all light emitted from lightelement 1801A illuminates substantially the entire active area 1851.Furthermore, according to one embodiment of the invention, theillumination is along a same direction. For example, light emitted fromlight element 1801A illuminates active area 1851 along direction 1810Aas exemplified by light rays 1811 and 1812, light emitted from lightelement 1801B illuminates active area 1851 along direction 1810B, andlight emitted from light element 1801C illuminates active area 1851along direction 1810C. Furthermore, according to one embodiment of theinvention, directions 1810A, 1810B, and 1810C are different from oneanother as shown in FIG. 19.

According to one embodiment of the invention, all light rays that areemitted along a same direction by a two-dimensional array ofindependently operable light elements converge substantially to a samelocation in the active area of a corresponding light modulator.

Each of the three exemplary illumination systems shown in FIG. 19 canprovide illumination in a same color or different colors. For example,illumination system 1801 can provide illumination in blue by, forexample, employing blue emitting light sources, or by incorporatingappropriate color filters not explicitly shown in FIG. 19. Similarly,illumination system 1802 can provide illumination in red, andillumination system 1803 can provide illumination in green.

Projection system 1800 further includes a color combiner 1860 forcombining and superimposing images formed by the three light modulators.FIG. 19 shows optically transmissive light modulators, such as opticallytransmissive LCDs. In some applications, the modulators can bereflective, (see, e.g., FIGS. 14 and 20) in which case color combiner1860 combines and superimposes reflected images formed by the lightmodulators.

Paths of images formed by the different light modulators areschematically shown in color combiner 1860. In particular, ray path 1861shows the general propagation path for an image formed by illuminationsystem 1801, ray path 1862 shows the general propagation path for animage formed by illumination system 1802, and ray path 1863 shows thegeneral propagation path for an image formed by illumination system1803. Although the ray paths are shown to be slightly offset relative toone another, this is done for ease of illustration. In general, imagesformed by the illumination systems substantially overlap and superimposeto form a colored image having high resolution.

Projection system 1800 further includes a projection lens system 1870and a projection screen 1880. Projection lens system 1870 typicallyincludes multiple lenses (for example, five in FIG. 19). Examples ofknown projection lens systems are discussed in U.S. Pat. Nos. 6,417,971;6,301,057; and 5,969,876.

Projection system 1800 may be a rear projection system, in which case,projection screen 1880 is preferably a rear projection screen.Projection system 1800 may be a front projection system, in which case,projection screen 1880 is preferably a front projection screen.

FIG. 20 shows a schematic side-view of a projection system 2000 inaccordance with one embodiment of the invention. Projection system 2000includes a first illumination system 2001, a second illumination system2002, and a third illumination system 2003, although, in general,projection system 2000 can have more or fewer illumination systems.Furthermore, although FIG. 20 shows the three illumination systemsgenerally arranged along x and y directions, in general, eachillumination system can be oriented in any direction as required in agiven application.

Each illumination system in FIG. 20 includes a two-dimensional array ofindependently operable light elements, a first lens array, and a secondlens array. For example, first illumination system 2001 includestwo-dimensional array of independently operable light elements 2010,three of which (light elements 2001A, 2001B, and 2001C) are shown inFIG. 20, a first lens array 2020, and a second lens array 2030. Ingeneral, the light elements in each two-dimensional array ofindependently operable light elements are arranged to optimally meet theneeds in a given application.

Furthermore, each light element in an illumination system has adedicated lens from a corresponding first lens array and a dedicatedlens from a corresponding second lens array. For example, light element2001C has dedicated lens 2020C from first lens array 2020 and dedicatedlens 2030C from second lens array 2030. The three illumination systemsshare the same field lens 2005 and the same reflective light modulator2050, where reflective light modulator 2050 has an active area 2051capable of displaying an image. Light modulator 2050 is preferably a DMDsuch as a DLP.

In the exemplary embodiment shown in FIG. 20, the illumination systemsshare light modulator 2050. In some applications, each illuminationsystem may have a dedicated light modulator.

According to one embodiment of the invention, light emitted by eachlight element illuminates substantially the entire active area of thelight modulator. For example, all light emitted from light element 2001Ailluminates substantially the entire active area 2051. Furthermore,according to one embodiment of the invention, light rays from a givenlight element illuminate active area 2051 along a same direction, wherethe direction of illumination is different for different light elementsin the same two-dimensional array of independently operable lightelements.

According to one embodiment of the invention, all light rays that areemitted along a same direction by a two-dimensional array ofindependently operable light elements converge substantially to a samelocation in active area 2051 of light modulator 2050.

Each of the three exemplary illumination systems shown in FIG. 20 canprovide illumination in a same color or different colors. For example,illumination system 2001 can provide illumination in blue by, forexample, employing blue emitting light sources, or by incorporatingappropriate color filters not explicitly shown in FIG. 20, illuminationsystem 2002 can provide illumination in red, and illumination system2003 can provide illumination in green.

Projection system 2000 further includes a color combiner 2060 shared bythe three illumination systems for compact and efficient redirecting oflight from different light elements to light modulator 2050. Ray pathsin color combiner 2060 are schematically shown in FIG. 20. Inparticular, path 2061 shows the general propagation path for light raysfrom illumination system 2001, path 2062 shows the general propagationpath for light rays from illumination system 2002, and path 2063 showsthe general propagation path for light rays from illumination system2003. Although the ray paths are shown to be slightly offset relative toone another, this is done for ease of illustration. In general, lightrays from the illumination systems are sufficiently overlapped toprovide efficient illumination of active area 2051.

Projection system 2000 further includes a total internal reflection(TIR) prism 2070 for compact and effective redirecting of light. TIRprism 2070 includes a first prism 2071, a second prism 2072, an inputface 2074, an exit face 2075, and a low index area 2073, such as air,for separating prism 2071 from prism 2072.

A ray of light 2081 entering first prism 2071 from input face 2074suffers total internal reflection at the interface between first prism2071 and low index area 2073 at point 2085, and propagates toward lightmodulator 2050 as light ray 2082. Light ray 2082 is incident on a pixelin active area 2051. If the pixel is in an “on” state, incident lightray 2082 is reflected back as ray 2083 that exits TIR prism 2070 fromexit face 2075 and propagates towards projection lens system 2090. If onthe other hand, the pixel is in an “off” state, incident light ray 2082is reflected as ray 2084 away from projection lens system 2090. Ray 2084is typically trapped by a light trap not shown in FIG. 20.

Projection system 2000 further includes a projection lens system 2090and a projection screen 2095. Projection lens system 2090 typicallyincludes multiple lenses (for example, five in FIG. 20). Examples ofknown projection lens systems are discussed in U.S. Pat. Nos. 6,417,971;6,301,057; and 5,969,876.

Projection system 2000 may be a rear projection system, in which case,projection screen 2095 is preferably a rear projection screen.Projection system 2000 may be a front projection system, in which case,projection screen 2095 is preferably a front projection screen.

Projection system 2000 further includes a processor 2024, similar toprocessor 1103 of FIG. 16, for determining, ranking, and storingcontrast ratios corresponding to each individual light element.Processor 2024 further determines an average intensity of a projectableimage formed by light modulator 2050, based on which, processors 2024may reduce the output intensity of one or more discrete light elementshaving low contrast ratios and/or increase the output intensity of oneor more other discrete light elements having high contrast ratios toimprove contrast ratio and/or brightness of the overall projectableimage.

All patents, patent applications, and other publications cited above areincorporated by reference into this document as if reproduced in full.While specific examples of the invention are described in detail aboveto facilitate explanation of various aspects of the invention, it shouldbe understood that the intention is not to limit the invention to thespecifics of the examples. Rather, the intention is to cover allmodifications, embodiments, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

1. An illumination system comprising: a plurality of discrete lightsources, an output light intensity of each discrete light source beingindividually controllable, at least one discrete light source emittingwhite light; and a pixelated light modulator having an active areadisplaying an image, wherein each discrete light source illuminatessubstantially the entire active area, and wherein a contrast ratio ofthe image is adjustable by controlling the output intensity of one ormore of the discrete light sources.
 2. The illumination system of claim1, wherein the plurality of discrete light sources form a circular arrayof discrete light sources.
 3. The illumination system of claim 1,wherein at least one of the plurality of discrete light sources is anLED.
 4. The illumination system of claim 1 further comprising anaperture stop positioned in a conjugate plane of the plurality ofdiscrete light sources.
 5. The illumination system of claim 4, whereinthe light from the plurality of discrete light sources substantiallyfills an entire opening of the aperture stop.
 6. The illumination systemof claim 4, wherein each of the plurality of discrete light sources isimaged within an opening of the aperture stop.
 7. The illuminationsystem of claim 1, wherein the pixelated light modulator comprises aliquid crystal modulator.
 8. The illumination system of claim 1, whereinthe pixelated light modulator comprises a digital micro-mirror device.9. The illumination system of claim 1, wherein the contrast ratio of theimage is made greater by reducing the output intensity of one or more ofthe outermost discrete light sources of the plurality of discrete lightsources.
 10. A projection display comprising one or more of theillumination system of claim
 1. 11. The projection display of claim 10being a front projection display.
 12. The projection display of claim 10being a rear projection display.
 13. The projection display of claim 10,wherein an image formed by the projection display is a virtual image.14. The illumination system of claim 1, wherein each discrete lightsource has a corresponding contrast ratio, and wherein the output lightintensity of one or more discrete light sources with corresponding lowcontrast ratios is reduced to increase the contrast ratio of the image.15. An illumination system comprising: a plurality of discrete lightsources, an output light intensity of each discrete light source beingindividually controllable; an aperture stop positioned in a conjugateplane of the plurality of discrete light sources; and a pixelated lightmodulator having an active area displaying an image, wherein eachdiscrete light source illuminates substantially the entire active area,and wherein a contrast ratio of the image is adjustable by controllingthe output intensity of one or more of the discrete light sources. 16.The illumination system of claim 15, wherein the light from theplurality of discrete light sources substantially fills an entireopening of the aperture stop.
 17. The illumination system of claim 15,wherein each of the plurality of discrete light sources is imaged withinan opening of the aperture stop.